Piston rings with coating impregnated with antifriction agent

ABSTRACT

A PISTON RING HAVING A BEARING FACE COATED WITH A HARD POROUS METAL OR METAL ALLOY HAVING ITS PORES IMPREGNATED WITH A SOLID ANTIFRICTION AGENT SUCH AS GRAPHITE. THE POROUS METAL OR METAL ALLOY HAS AN OPEN POROSITY RANGING FROM ABOUT 7 TO ABOUT 30% BY VOLUME OF THE OUTER SURFACE OF THE COATED BEARING FACE, AND THE PORE OPENINGS RANGE FROM ABOUT 0.2 MICRON TO ABOUT 10 MICRONS, THEREBY BEING LARGE ENOUGH TO DISCHARGE THE ANTIFRICTION AGENT TO THE CYLINDER SURFACE FOR LONG PERIODS OF TIME AFTER THE ANTIFRICITION COATING WEARS OFF OF THE BEARING FACE AND THHE METAL OR METAL ALLOY RIDES ON THE CYLINDER WALL. AT THE SAME TIME THE PORES ARE SUFFICIENTLY SMALL TO PREVENT ACCUMULATION AND TRAPPING OR DEBRIS SUCH AS MIGHT BE FORMED DURING THE BREAK-IN PERIOD OF OPERATION OF THE ENGINE. PREFERRED HARD POROUS METAL AND METAL ALLOY COATINGS ARE MOLYBDENUM, MOLYBDENUM ALLOYS AND TUNGSTEN CARBIDE ALLOYS.   D R A W I N G

PISTON RINGS WITH COATING IMPREGNATED WITH ANTIFRICTION AGENT OriginalFiled Oct. 20, 1969 3 SheetS-Sheet 1 INVENTOR ATTYS.

H. F. PRASSE Jul al, 1973 3 Sheets-Sheet 2 Original Filed Oct. 20, 19690 1 x l a w 0 a w WW m D w P 5 5 I w M a I W I l 5 I 0 1 w y m I. 0 0 0m 0 m a w w 2 0 QfimGk NQMQ m w w w w a w 0 IN VENTOR.

July 31, 1973 H. F. PRASSE 3,749,559

PISTON RINGS WITH COATING IMPREGNATED WITH ANTIFRIC'IION AGENT 3Sheets-Sheet 5 Original Filed Oct. 20, 1969 IN VEN TOR.

zfi'szeef FP Q2952? 3 749 559 PISTON RINGS WITH COATING IMPREGNATED WITHANTIFRICTION AGENT Herbert F. Prasse, Town and Country, Mo., assignor toRamsey Corporation, St. Louis, Mo.

Original application Oct. 20, 1969, Ser. No. 867,632, now Patent No.3,617,349. Divided and this application June 29, 1971, Ser. No. 157,930

Int. Cl. F02f 5/00 U.S. Cl. 29-191.2 11 Claims ABSTRACT OF THEDISCLOSURE A piston ring having a bearing face coated with a hard porousmetal or metal alloy having its pores impregnated with a solidantifriction agent such as graphite. The porous metal or metal alloy hasan open porosity ranging from about 7 to about 30% by volume of theouter surface of the coated bearing face, and the pore openings rangefrom about 0.2 micron to about 10 microns, thereby being large enough todischarge the antifriction agent to the cylinder surface for longperiods of time after the antifriction coating wears off of the bearingface and the metal or metal alloy rides on the cylinder wall. At thesame time the pores are sufficiently small to prevent accumulation andtrapping or debris such as might be formed during the break-in period ofoperation of the engine. Preferred hard porous metal and metal alloycoatings are molybdenum, molybdenum alloys and tungsten carbide alloys.

RELATED APPLICATION This application is a division of my copending U.S.application entitled Method of Making Anti-Friction Piston Rings, Ser.No. 867,632 filed Oct. 20, 1969 (now Pat. No. 3,617,349, dated Jan. 2,1971).

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates to the packing ring or piston ring art and to the provision ofbearing faces on piston rings. The invention particularly deals withcoatings on piston rings which exhibit exceptional antifrictioncharacterstics, particularly valuable in the start-up operating periodof internal combustion engines.

Description of the prior art One of the most critical times for theoperation of the cylinder-piston assembly of an internal combustionengine is during its initial operation or break-in period. During thispreliminary engine operation there are a number of physical and perhapschemical changes of the running surfaces of the piston rings andcylinder barrels. After this period of time usually, say about 1000miles, the properties of the surfaces of the piston rings and cylinderbore have been altered which should then result in optimum performancecharacteristics. It is during this initial period of time that a pistonring including both compresson and oil control rings should exhibitmaximumu antifriction or scuff resistance properties.

To achieve close fit with piston rings cylinder bores are normally honedor polished. However, it has been found that this operation does presenta drawback in that the graphite pockets in the cylinder normally leadingto the surfaces have been closed. Therefore, the nat- United StatesPatent O "ice ural antifriction property of the cylinder has beensubstantialy lessened.

To overcome the above, it has been proposed that the bearing face of apiston ring be coated with a dry film lubricant such as graphite.However, the surface. coating is quickly obliterated after a relativelyshort period of engine operation, and the desired antifriction propertylost. Chances for scufling are then materially greatened.

It would therefore be a substantial advance in the art if a piston ringwere discovered which had a hard wearing surface and yet exhibited thedesired antifriction property, particularly during the time of enginebreak-in but also beyond that point.

SUMMARY OF THE INVENTION The present invention provides hard-facedpiston rings which also exhibit long term antifriction properties ofite. The concept of impregnation is particularly important in order toprovide a long lasting period of lubrication, particularly during theinitial period of engine break-in. A mere lubricant coating of the metalcoated bearing face is ineffectual by reason of its being used up priorto the termination of the break-in period.

The piston rings of this invention are preferably made according to themethod of my aforesaid Pat. No. 3,617,- 349. This method includes thesteps of coating the bear ing face of a piston ring with a hard porousmetal or metal alloy. The coated ring is then heated to drive the airfrom the pores of the coating. The still hot piston ring is thencontacted with an antifriction agent which is dissolved or dispersed ina liquid solvent acting as a carrier. Upon contact of the ring theantifriction agent is drawn into the pores of the coating and remainstherein as an impregnant of the coating. Meanwhile, the liquid carriercontacting the hot surface of the piston ring is volatilized from thering.

It is therefore the object of the invention to provide an improvedpiston ring.

A more specific object of the invention is to provide a piston ringhaving its bearing face treated such that it exhibits both long wear inuse, and as well demonstrates excellent lubricity, particularly duringthe engine breakin period, therefore substantially lessening cylinderscuffing leading to engine failure.

A still further object of the invention is to provide the aboveantifriction ring whereby engine torque can be materially reduced whencompared to like use of prior art coated piston rings. 7

Other objects, features and advantages ofithe invention will be readilyapparent from the following description of certain preferred embodimentsthereof, taken in conjunction with the accompanying drawings, althoughvariations and modifications may be effected without departing from thespirit and scope of the novel concepts of the disclosure, and in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a photomicrograph of thesurface of a cylinder after honing prior to operation;

FIG. 2 is a photomicrograph of a cylinder surface after a period ofoperation;

FIG. 3 is a graph relating engine speed to friction horsepower with apiston ring of the invention compared to a prior art piston ring;

FIG. 4 is a graph comparing static break-away torque utilizing a pistonring of the invention compared to prior art piston rings;

FIG. 5 is a side elevational view, with parts in crosssection, of anengine piston and cylinder assembly, wherein the piston has ring groovesequipped with compression and oil control rings, each having a bearingface engaging the cylinder which is composed of an 'm situ formed plasmajet applied coating;

FIG. 6 is an enlarged fragmentary crosssectional view of the topcompression ring in the piston of FIG. 5;

FIG. 7 is a view similar to FIG. 6, illustrating the second compressionring in the piston of FIG. 5;

FIG. 8 is a view similar to FIG. 6 but illustrating the oil control ringin the third ring groove of the piston of FIG. 5;

FIG. 9 is a view similar to FIG. 6, but illustrating the oil controlring in the fourth ring groove of the piston of FIG. 5; and

FIG. 10 is an elevat-ional view of an arbor of piston rings being plasmajet coated.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As noted above, the pistonrings of the invention are those having a bearing face coated with ahard porous metal or metal alloy. impregnated in the pores of the metalis an antifriction agent.

The piston ring may be first coated with the metal or metal alloy in anyconventional manner, although, it is greatly preferred that the pistonrings be coated utilizing a plasma jet spray technique, as will bediscussed in more detail hereinafter. The coating itself may be derivedfrom a number of metal or metal alloys with the only requirement beingthat it have sufficient porosity to absorb a substantial amount of theantifriction agent. Base coatings which may be utilized hereinclude suchcoatings as molybdenum, molybdenum alloys, tungsten carbide alloys,chromium carbide alloys, alumina-titania, zirconium oxide, etc. For bestresults the porous metal or metal alloy should have an open porosityranging from about 7% to about 30% by volume of the outer surface of thethuscoated bearing face. More often, the porosity ranges from about 7%to about 20%. Again, the pore opening should be sufiiciently large toallow sufiicient inclusion of the antifriction agent. Normally the poreopenings range from about 0.2 micron to about 10 microns. Preferredcoatings include molybdenum, molybdenum alloys, and tungsten carbidealloys.

As mentioned above, the initial or base coatings are preferably appliedby resort to a plasma jet spray procedure wherein the coating is formedin situ on the hearing face of the ring. The coating is usually appliedby resort to a powder containing the various metals or metal alloys aspowder ingredients.

A typical coating will be formed from a powder containing tungstencarbide and other metals as follows:

25 to 55% by weight tungsten carbide 4 to 8% by weight cobalt 25 to 45%by weight nickel 3 to 7% by Weight chromium 0 to '7 by weight aluminum 0to 3% by weight boron Balance-substantially iron.

The tungsten carbide content of the above powder may be admixed with orreplaced by other carbides such as the carbides of metals or metalloidsfrom the group including titanium, tantalum, columbium, molybdenum,

vanadium, chromium, zirconium, hafnium, silicon, and boron.

A specific tungsten carbide powder is a mixture of the followingcompositions:

Other and preferred coatings are molybdenum-derived coatings, eithermolybdenum itself or a molybdenum alloy. One molybdenum powder has thefollowing composition:

65% to 90% by weight molybdenum 7% to 25% by weight nickel 1% to 6% byWeight chromium 0.3% to 1.5% by weight boron 0.2% to 1.5% by weightsilicon Balance-iron with small amounts of carbon and cobalt.

A preferred molybdenum powder has the following range of elements:

65% to 90% by weight of molybdenum 7% to 24.5% by weight of nickel 1.6%to 5.8% by weight of chromium 0.4% to 1.3% by weight of boron 0.3% to1.4% by weight of silicon Balanceiron with small amounts of carbon andcobalt.

One specifically preferred powder mixture has the following composition:

75% by Weight molybdenum 17.5% by weight nickel 4.12% by weight chromium0.94% by weight boron 1.00% by weight silicon Balance-iron with smallamounts of carbon and cobalt.

Another preferred powder has the following range of elements:

65 to 90% by weight of molybdenum 3.5 to 12% by weight of nickel 3 to10% by weight of chromium 1.5 to 5% by weight of tungsten 1 to 3% byweight of cobalt 0.8 to 3% by weight of iron 0.2 to 1% by Weight ofcarbon Balancesilicon and manganese.

One specific powder mixture falling within the above range has thefollowing composition:

% by weight molybdenum 7% by weight nickel 6% by weight chromium 3% byWeight tungsten 2% by weight cobalt 0.8% by weight iron 0.4% by weightcarbon Balance-silicon and manganese.

A still further preferred powder mixture has the following range ofelements:

65 to by weight of molybdenum 6.5 to 25% by weight of nickel 1.3 to 7%by weight of chromium 0.3 to 1.7% by weight of silicon 0.2 to 1.7 byweight of boron 0.3 to 1.7% by weight of iron 0.1 to 0.4% by weight ofcobalt Balance-carbon and manganese.

Another specific powder mixture falling within the just-enumerated rangeof elements has the following composition:

80% by weight molybdenum 14.6% by weight nickel 2.8% by weight chromium0.8% by weight silicon 0.6% by weight boron 0.7% by weight iron 0.2% byweight cobalt Balancecarbon and manganese.

After the piston ring has been properly coated with a porous type ofcoating, it is then impregnated with an antifriction agent. This iscarried out by first heating the coated piston ring to say 300400 F. todrive the air from the pores of the coating. Immediately thereafterwhile the ring is still hot it is contacted with a solution ordispersion of the antifriction agent. The antifriction agent is thendrawn into the pores of the coating, remaining there as an impregnant,while the liquid carrier is evaporated upon contacting the hot pistonring.

The actual contact step of ring and antifriction agent may be carriedout via a variety of techniques such as spraying the antifriction agenton the hot ring or immersing the ring in a solution or dispersioncontaining the antifriction agent.

The antifriction agent may be chosen from a wide variety of materialsincluding such lubricants as graphite, zinc stearate, mica, fibroustalc, magnesium oleate, calcium palmitate, barium stearate, molybdenumsulfide, aluminum sulfide, Teflon, and combinations of the above. Apreferred antifriction agent is graphite.

Again, the solvent or dispersing medium for any one or more of the aboveantifriction agents may be chosen from a wide variety of liquids such asalcohols, benzene, toluene, xylene, aliphatics, esters, ethers,halogenated hydrocarbons, kerosene, substituted benzenes, etc. Forexample, a typical solvent for graphite is mineral spirits.

After the above steps have been followed the thus impregnated ringcoating is ready for use. A suflicient amount of antifriction agent ispresent in the coating to last at least through the break-in period ofthe engine. The friction level is then maintained at a low level andtemperature problems are avoided. Piston rings containing the dry filmlubricant or antifriction agent may be employed in diesel engines andgasoline engines, giving equally good protection in both. After theinitial break-in period, usually considered to be at least 1000 miles,the graphite begins to be exposed in the cylinder bore itself. Untilthis time the antifriction agent such as graphite from the ring isprovided for proper protection.

The antifriction rings of the invention are particularly useful in lowemission engines. In engines of this type which remain hot afterstopping it is imperative to have a relatively high cranking speed.Thus, one needs low friction rings in order to crank the engine fastenough with current ordinary batteries.

Turning now to the drawings, FIG. 1 is a photomicrograph of the surfaceof a cylinder after being honed. The pockets near the surface have beenclosed by the honing operation. In this regard it is interesting to notethat up to about 1000 miles of use the cylinder bores did not exhibitgraphite pockets even at the turn-around point of the ring, which is thearea of most wear. Thus, during the critical break-in period and forsome time thereafter the graphite of the cylinder would not be availableas an antifriction agent. It is evident then that the impregnated pistonring coatings of the invention are extremely useful during this period.

FIG. 2 is a photomicrograph showing a portion of a cylinder surface inring travel after about 1000 hours of operation. The magnification herewas again 750 times. It is evident now that graphite pockets areavailable at the surface of the cylinder, and the graphite available asa dry lubricant. However, as noted above, prior to about 300 hours ofwear the graphite was not available due to honing of the cylinder.

FIG. 3 is a graph showing the reduced friction at various engine speedsutilizing a graphite impregnated molybdenum coated piston rings versus anon-impregnated molybdenum piston ring. In Test I, involving amolybdenum coated ring, engine speeds at various r.p.m.s are plottedagainst friction horsepower as a dotted line. A like plot is shown as asolid line involving a graphiteimpregnated molybdenum ring in Test II.It is clearly evident that the graphite impregnation materially reducedfriction due to pressure of the antifriction agent, here 'beinggraphite.

FIG. 4 again shows improved engine performance using a graphiteimpregnated ring. Here, static break-away torque was compared with threerings. The first was a barrel face chrome compression ring designated onthe graph as I. The second was a barrel face molybdenum compression ringdesignated as II on the graph. The third was a piston ring of theinvention, here a barrel face molybdenum graphite-impregnatedcompression ring designated III. It is apparent from the graph of FIG.4, that there is required a hundred percent increase in relative torquein an engine utilizing a chrome compression ring compared to a likeengine wherein there is employed a graphite-impregnated molybdenumcoated ring. Likewise, there is greater than a 50% increase in relativetorque utilizing a molybdenum coated compression ring versus thegraphite impregnated molybdenum coated compression ring of theinvention. Again, the antifriction property of the rings of theinvention is amply demonstrated in this work.

The remaining figures, FIGS. 5-10, illustrate typical piston rings whichmay be coated, coated rings thereof, and the preferred method of coatingthese rings by plasma jet coating techniques.

The piston and cylinder assembly 10 of FIG. 5 illustrates generally aconventional 4-ring groove internal combustion engine piston, operatingin an engine cylinder. The assembly 10 includes a piston 11 and anengine cylinder 12 with a bore 13, receiving the piston 11. The piston11 has a head 14 with a ring band 15 having four peripheral ring grooves16, 17, 18 and 19 therearound. The top ring groove 16 has a split solidcast iron compression or fire piston ring 20 therein. The second ringgroove 17 has a split solid second compression ring 21 somewhat widerthan the ring 20. The third ring groove 18 carries a tWopiece oilcontrol ring assembly 22. The fourth or bottom ring groove 19 carries athree-piece oil control ring assembly 23.

As shown in FIG. 6, the top compression or fire ring 20 has a main body24 composed of cast iron. preferably nodular gray iron, with a carboncontent of about 3% percent by weight. The outer periphery 25 of thisring is covered with a hard refractory coating 26, which may be, forexample, a plasma jet applied molybdenum or molybdenum alloy coating.

As shown in FIG. 7, the second compression ring 21 has a main body 27composed of the same type of cast iron as the body 24 of the ring 20.The outer periphery 28 of the body 27 is inclined upwardly and inwardlyfrom the bottom edge of the ring, and a peripheral groove 29 is formedaround this inclined periphery. The groove 29 is filled with the coating26.

As shown in FIG. 8, the oil control ring assembly 22 in the third ringgroove 18 is composed of a one-piece flexible channel ring 30 and asheet-metal expander ring 31, having legs extending into the channel forexpanding the ring 30. The ring 30' and the expander are more fullydescribed in Mayhew et al. Pat. 3,281,156.

The one-piece control ring 30 has a pair of axially spaced, radiallyprojecting beads 3-2. The peripheries of these beads 32 are coated withthe coating 26-.

In FIG. 9, the oil control ring assembly 23 includes a resilientspacer-expander ring 33 supporting and expanding split thin rail rings34. The assembly 33 is of the type disclosed in Marien US. Pat.3,133,739. The outer peripheries of the rail rings 34 are coated withthe coating 26.

From the above description, it will be understood that the bearing facesof each of the compression and oil control rings 20, 21, 22 and 23 arecoated with some hard facing prior to being impregnated with anantifriction agent. These bearing faces 26 ride on and sealingly engagethe bore 13 of the engine cylinder 12, and the rings are compressed inthe bore 13, so as to expand tightly against the bore wall, and maintaina good sealing sliding engagement therewith.

As shown in FIG. 10, the coatings 26 are applied on the rings as forexample on the grooved rings 21 by stacking a plurality of the rings onan arbor 35, with the rings compressed so that their split ends will bein abutment. The arbor clamping the stack of rings in their closed,contracted position may be mounted in a lathe and the peripheries of therings machined to form the grooves 29 therearound. The outer peripheriesof the rings 21 on the arbor are then coated with the coatings 26 from aplasma jet spray gun 36. The gun 36 includes an insulated casing such asnylon 37, from which projects a rear electrode 38, the projection ofwhich is adjustably controlled by a screw knob 39. The front face of thecasing receives a front electrode 40. The casing 37 and electrode 40 arehollow and water-jacketed so that coolant may circulate therethroughfrom an inlet 41 to an outlet 42. Plasma jet gas is fed through an inlet43 into the chamber provided by the casing 37 and the electrode 40 toflow around the electrode 38.

The front end of the electrode 40 provides a nozzle outlet 44 for theplasma flame and the ingredients to form the coating 26 are fed to thisnozzle through a powder inlet 45, just in advance of the dischargeoutlet of the nozzle.

A plasma composed of ionized gas is produced by passing the plasma gasfrom the inlet 42 through an electric are established between theelectrodes 38 and 40. This plasma gas is non-oxidizing and may becomposed of nitrogen and hydrogen with argon, or helium as a carrier.The plasma flame exuding from the nozzle 44 draws the powder therewithby aspiration and subjects the powder ingredients to high temperaturesto cause them to melt. The jet stream carries the melted metal into thebottom of the groove 29 of each piston ring and fills the groove.

. After the coating is deposited it is bound to the base body of thering of the piston. The fused-in coating forms in situ in the groove ofthe piston ring and is bonded to the body of the ring along a fusedinterface or welded zone. The interface or zone is composed of materialsof the coating and the material of the ring body.

During the jet spray application it is desired to maintain a temperaturein the groove of the piston ring such that excessive burning and meltingaway of the body metal is prevented. To achieve this end result, thearbor of the rings is preferably cooled with an external blast of inertgas impinging on both sides of the jet flame. It is desirable to keepthe temperatures of the rings in the arbor around 400 F. or less. It isnot necessary to provide any subsequent heat treatment for the plasmajet coated rings other than allowing the rings to air cool.

The powder fed to the inlet of the plasma jet spray gun is meteredpreferably with the aid of an aspirating gas, vibration, mechanicalgearing, etc. All the powder is completely melted and penetrates intothe center cone of the plasma jet flame.

The following examples illustrates a typical method for preparing theanti-friction impregnated rings of the invention. Of course, thisexample is merely illustrative, and the invention is not to be limitedthereto.

8 EXAMPLE 1 A piston ring was first prepared with a pure molybdenumcoating applied via the plasma jet spray technique described above. Anumber of rings were prepared in this manner constituting an arbor ofrings. The molybdenum coatings had pore openings ranging from about 0.2micron to about 10 microns and an open porosity of about 20% by volume.

A dispersion of an antifriction agent comprising graphite in mineralspirits was then prepared. Specifically, a commercial preparation of a50% solids content of graphite dispersed in a mineral spirits carrierwas further diluted. One gallon of the graphite dispersion was dilutedwith two gallons of mineral spirits, and thoroughly agitated to insure ahomogeneous mixture.

The arbor of rings was placed in a preheated oven at 350 F. for 10minutes. After 10 minutes the arbor of rings was removed from the ovenand immediately sprayed with the diluted graphite solution. The graphiteupon contacting the hot rings was absorbed into the pores of the ringcoatings while the mineral spirits vehicle was evaporated from therings. The arbor was then unloaded, the rings separated and dried for 30minutes.

It is evident that this invention provides unique antifriction pistonrings. The piston rings have particular utility in lessening frictionand increasing scuff resistance during the critical period of enginebreak-in.

I claim as my invention:

1. A piston ring having a bearing face coated with a hard porous metalor metal alloy having an open porosity at its outer surface of about 7to about 30% by volume and a pore opening of about 0.2 to about 10microns, and a solid antifriction agent impregnated in said pores.

2. The piston ring of claim 1 wherein said anti-friction agent isgraphite.

3. The piston ring of claim 1 wherein said coating is a molybdenumcoating.

4. The piston ring of claim 1 wherein said coating is a molybdenum alloycoating.

5. The piston ring of claim 1 wherein said coating is a tungsten carbidealloy coating.

6. The piston ring of claim 1 where said metal or metal alloy coating isa plasma jet applied coating.

7. The piston ring of claim 6 wherein said coating is formed in situ onthe bearing face.

8. A seal for engines which comprises a metal body member with a sealingface bonded to said body member composed of a hard porous metal or metalalloy with a thin overlying coating of a solid antifriction agent thatwears away during an initial break-in period of operation of the seal inan engine to expose the porous metal or metal alloy coating as the sealface, said porous metal or metal alloy coating having an open porosityat its outer surface of about 7 to about 30% by volume and a poreopening size of about 0.2 to about 10 microns which remains open afterthe break-in period of operation, and a solid anti-friction agentimpregnated into said pores for continuing the antifriction lubricationof the sealing interface between the hard porous metal or metal alloyand the engine Wall after the antifriction coating wears off of thesealing face.

9. A piston ring having a bearing face coated with an in situ formedplasma jet spray applied coating formed from a mixture of the followingcomposition:

20 to 55% by weight of a carbide selected from the group consisting ofcarbides of tungsten, titanium, tantalum, columbium, molybdenum,vanadium, chr0- mium, zirconium, hafnium, silicon and boron 4 to 8% byweight cobalt 25 to 45% by weight nickel 3 to 7% by weight chromium 0 to7% by weight aluminum 0 to 3% by weight boron Balancesubstantially iron,

said coating having an open porosity at its outer surface of about 7 toabout 30% by volume and a pore opening size of about 0.2 to aboutmicrons, and a solid antifriction agent impregnated in said pores.

10. A piston ring having a bearing face coated with an in situ formedplasma jet spray applied porous coating formed from a mixture of thefollowing composition:

65% to 90% by weight molybdenum 7% to by weight nickel 1% to 6% byWeight chromium 0.3% to 1.5% by weight boron 0.2% to 1.5% by weightsilicon Balance-iron with small amounts of carbon and cobalt, saidcoating having an open porosity at its outer surface of about 7 to aboutby volume and a pore opening size of about 0.2 to about 10 microns, anda solid antifriction agent impregnated in said pores.

11. The piston ring of claim 10 wherein the coating is formed from apowder composed of the following ingredients:

to by weight of molybdenum 3.5 to 12% by weight of nickel 10 3 to 10% byweight of chromium 1.5 to 5% by weight of tungsten 1 to 3% by weight ofcobalt 0.8 to 3% by weight of iron 0.2 to 1% by weight of carbonBalance-silicon and manganese.

References Cited UNITED STATES PATENTS L. DEWAYNE RUTLEDGE, PrimaryExaminer M. J. ANDREWS, Assistant Examiner US. Cl. X.R.

